Linear actuator

ABSTRACT

A linear actuator includes an inner section that moves within an outer section. The inside of the outer section includes racks and the outside of the inner section includes pinions that engage the racks. Two pairs of racks and pinions are positioned at an angle of 90° with respect to each other. The outer section includes at least two pairs of sides located opposite to one another and one of the racks is mounted on each of the sides.

BACKGROUND OF THE INVENTION

The present invention relates to a linear actuator comprising an outersection having a longitudinal axis and an inner structure which isfitted inside the outer section and is movable with respect thereto inthe direction of said longitudinal axis.

An actuator of this type is generally known in the prior art. Pneumaticand hydraulic cylinders are used for moving all kinds of componentswhich are movable with respect to one another. Motor-driven structuresare also known.

There is a need, for furniture, such as chairs, desks and otherapplications, for an actuator which in the smallest position has a smallstructural height, with which there is no play between the innerstructure and the outer section in any of the extended positions, whichis simple and inexpensive to produce and including an autonomous drive.

SUMMARY OF THE INVENTION

This aim is realised with an actuator as described above in that theouter section is provided with at least two racks which extend in thedirection of said longitudinal axis and the inner structure comprises anequal number of pinions engaging on the racks, said pinions beingmechanically linked and at least one pinion being drivable by a motormounted in said inner structure in order to achieve operation of saidactuator.

The invention is based on the insight of providing the inner structurewith an (electric) drive motor. This motor drives at least one pinion.Further pinions are fitted in order to provide accurate guiding of theinner section with respect to the outer section. If, in accordance withan advantageous embodiment of the invention, both the outer section andthe inner structure are constructed as square tubular sections, it isadvantageous that two drive pinions are provided which are mounted closeto the mid-points of two opposing sides, as well as two auxiliarypinions which take up play and which are likewise mounted opposite oneanother on the two mid-points of the two adjoining sides. In such a casethe first-mentioned and the last-mentioned pinions are coupled to oneanother by a connecting shaft. It has been found that in this way aparticularly small space requirement coupled with an appreciable strokecan be obtained with a compact motor. It has also been found thatnegligible play between the inner structure and the outer section occursthroughout said stroke and a particularly rigid unit is produced.

It is possible for two pinions/racks to suffice. However, according toan advantageous embodiment of the invention at least three racks and anequal number of pinions are provided, at least two of said pinions beingmechanically coupled.

Retaining means which provide for positioning of the inner structure andthe outer section with respect to one another can be provided asadditional elements to take up possible play. This retaining means can,for example, be arranged to provide fixed engagement between thenon-driven pinions and the rack concerned. Furthermore, it is possibleto choose the thickness of the racks such that the inner structure isheld in position with respect to the outer section.

Although it has been described above that both the outer section and theinner structure are constructed as square tubular sections, it must beunderstood that any other shape imaginable in the prior art is possible.Such a shape varies from triangular to polygonal and from circular toelliptical, it not being necessary for the outer section to have a shapewhich is congruent with the shape of the inner structure. The motordescribed above can be any motor known from the prior art, but anelectric motor that drives the pinions concerned, with or without theaid of a transmission, is preferred. By this means it is possible toprovide a very compact structure, with which appreciable loads can bemoved, with a small space requirement. An actuator of this type can, forexample, be used for the column of a chair or also for adjusting desks.It must be understood that this is merely an example and that many otherapplications of the actuator according to the present invention areconceivable.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference toan illustrative embodiment shown in the drawing. In the drawing:

FIG. 1 shows an exposed view of the actuator according to the inventionin a first extended position;

FIG. 2 shows a perspective view of the actuator according to FIG. 1 inthe retracted position;

FIG. 3 shows a top view of the actuator according to the invention; and

FIG. 4 shows a first variant of the actuator according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 the linear actuator according to the invention is indicated inits entirety by 1. This actuator consists of an outer section 2, whichin this embodiment has been constructed as a square tubular section. Atubular section that is likewise square and that acts as inner sectionand is indicated by 3 is fitted inside the outer section 2. The innersection 3 is so much smaller than the outer section 2 that racks 4 and5, which are mounted on the outer section, can be accommodated betweenthe two sections. Racks 4 engage with pinions 7, which are joined to oneanother via a shaft 10, whilst the racks 5 are engaged by pinions 8which are joined, for example by means of a keyway, to shaft 11. Thereare openings 17 in the inner section 3 to allow shafts 10 and 11 to befed through. A sprocket 12 is mounted on shaft 10, a chain 13, which isengaged by gear 14, running over sprocket 12 and, via worm transmission15, electric motor 16 drives pinions 7. Pinions 7 are driven intoengagement with rack 4 by the presence of retaining blocks 9, which arefirmly mounted on opposing outer sides of the inner section.

Movement of the inner section 3 with respect to the outer section 2takes place in accordance with a longitudinal axis 6. By operation ofmotor 16, pinions 7 are driven and movement with respect to the racks 4takes place. As a result of the presence of pinions 8, which are coupledto one another via shaft 11 and, moreover, engage on racks 5, it hasbeen found that a low-play rigid structure is produced, the innersection 3 displaying virtually no play with respect to the outer section2. As a result of the worm transmission in transmission 15, aself-braking structure is produced, that is to say movement of the innersection with respect to the outer section is possible only by operationof motor 16.

It will be understood that it is not necessary for the inventive conceptfor two pinions 8 located opposite one another to be present. Forinstance, it is possible to construct both the outer section 2 and theinner section 3 in the form of a U-section. It must also be understoodthat any other shape differing from the square or U-shape is possible.The motor 16 used, which can be any motor known from the prior art, ispreferably a so-called windscreen wiper motor which can be controlled bya relatively low voltage and develops appreciable power for smallinstallation dimensions and a low cost price.

FIG. 4 shows a further variant of the invention in which only twopinions/racks are used. This actuator is indicated in its entirely by 21and consists of an inner section 23 and an outer section 22. The outersection 22 is provided with racks 24, 25, close to each end thereof,whilst the angular inner section is provided with pinions 27, 28 locatedtowards the inside. With this arrangement, pinion 27 is driven directlyby motor 30 through shaft 32, which on the other side is provided with aconical gear 29, which is in engagement with conical gear 26 to whichpinion 28 is connected through shaft 34. This structure isself-retaining and is found to have surprisingly little play.

It sill be understood that many variants of the actuator described aboveare possible. Numerous structural details can be modified without goingbeyond the scope of the present application. Moreover, it must beunderstood that the linear actuator described above has numerouspossible applications. All such variants and applications are consideredto fall within the scope of the appended claims and have theabovementioned advantages, these being a high (radial) rigidity of theactuator in both the retracted and the extended position, whilst it ispossible to produce a relatively high lifting force.

What is claimed is:
 1. Linear actuator (1, 2) comprising: an outersection (2, 22) having a longitudinal axis (6); an inner structure whichis mounted inside the outer section and is movable with respect theretoin the direction of said longitudinal axis, wherein the outer section(2, 22) is provided with at least two racks (4, 5, 24, 25) which extendin the direction of said longitudinal axis and the inner structurecomprises an equal number of pinions (7, 8, 27, 28) engaging on theracks, said pinions (7, 8, 27, 28) being mechanically linked and atleast one pinion (7, 27) being drivable by a motor (16, 30) mounted insaid inner structure in order to achieve operations of said actuator,wherein said outer section (2) comprises at least two pairs of sideslocated opposite one another and one of said racks is mounted on each ofsaid sides.
 2. Actuator according to claim 1, wherein at least threeracks (4, 5) and pinions (7, 8) are provided, at least two of saidpinions being mechanically coupled.
 3. Actuator according to claim 1,wherein retaining means (9) which provide for positioning of the innerstructure and the outer section are provided.
 4. Actuator according toclaim 3, wherein said retaining means (9) fix the position of the pinion(7) and the rack (4) with respect to one another.
 5. Actuator accordingto claim 1, wherein said outer section (2) is a closed section. 6.Actuator according to claim 1, wherein the pinions (7, 8) locatedopposite one another are always mechanically linked.
 7. Actuatoraccording to claim 1, wherein the inner structure comprises a section(3) within which said motor (16) is accommodated.
 8. Actuator accordingto claim 7, wherein said inner section comprises a closed sectionprovided with openings through which connecting shafts (10, 11) for apair of pinions extend.
 9. Actuator according to claim 2, whereinretaining means (9) which provide for positioning of the inner structureand the outer section are provided.